Environmental enrichment (EE) in the laboratory context is the process of improving the conditions of animal housing to provide stimulation. In this laboratory there is frequent review and improvement of the environmental conditions of laboratory animals while ensuring the scientific objectives of studies are met. In the last few years, in addition to wood chip bedding, aspen wood blocks for chewing have been provided for rats in this laboratory. The incidence of spontaneous tumours in control animals is used to interpret findings in treated animals in carcinogenicity studies. Therefore relevant and well-controlled historical background data are vital to the interpretation of findings. In order to determine the impact of EE items on spontaneous tumour incidence, a preliminary comparison was performed. Common spontaneous tumour incidences (>5%) from multiple housed (single supplier) Han Wistar rat 2-year carcinogenicity studies where EE was provided (n = 4) were compared with those without EE (n = 7) by Student’s t-tests. In studies with EE there was no statistical difference in the incidence of tumours in males or females from those without. In this preliminary investigation there was no impact of EE on tumour incidence. As more data become available a further investigation will be undertaken to determine the impact of EE on rat and mouse tumour incidences.
